Printing is the art and technology of reproducing words and pictures on paper, cloth, or other surfaces. Although there is a considerable variation in printing methods, printing typically involves a printing press that transfers an image from a printing plate or similar image-bearing surface to the material being printed.
Generally, printing presses are used for high-speed, high volume reproduction, especially to print books, newspapers, magazines, leaflets, wallpaper, posters and a number of other items.
In the 15th Century, the first printing press was invented by Johann Gutenberg, a German printer. Even though the art of printing has been known, at least in the Far East, for centuries, Gutenberg revolutionized and put together all the work of his predecessors to develop new techniques and invent the method that laid the foundation for all future printing.
Since then, a number of new and improved printing presses have been developed. For example in the early to mid-1800's the cylinder press (1810), the power press (1822) and the rotary press (1846) were invented. These types of presses are otherwise referred to as letterpress machines.
In addition to these letterpress machines, other printing methods such as gravure, offset lithography and screen-process were introduced. Lithography, for example, which is the process of printing from a plane surface on which the image to be printed is ink-receptive and the blanket area ink-repellant, was invented by Alois Senefelder of Prague in the late 1700's. The offset principle of transferring the image to paper by use of rubber blanket cylinders was invented by Ira Rubel, an American printer, about 1905.
In modern times major innovations in the printing industry have been developed which have revolutionized printing as we know it today. These innovations include the development of photo-typesetters, computers for automatic justification and hyphenation, electronic scanning machines for use in color printing, and electrostatic screen printing.
Nevertheless, in machine printing, offset lithography is still one of the most common processes used today, mainly because of its platemaking economics.
Generally, a printing machine carries out three processes: (1) it applies ink to a printing surface; (2) it applies pressure to transfer the ink to paper or some other material; and (3) it moves and holds the material so that every printed image is positioned accurately.
For example, an offset printing press (10'), as shown in FIG. 1, is comprised of a thin metal plate which is carried on a plate cylinder (12'). Associated with the plate cylinder (12') are two sets of rollers. As the plate cylinder (12') turns and before it is linked, the plate cylinder (12') is first wet by the first set of rollers (14') called the dampening system. At this stage of the printing process the non-image areas will repel the ink. The second set of rollers (16'), called the inking system, then applies the ink to the image areas. A blanket cylinder (18') then picks up the image of the plate and prints it on one side of a piece of paper (20') passing through the blanket cylinder (18') and an impression cylinder (22'). The blanket cylinder (18') is also referred to as a rubber printing blanket since it is typically made of canvas covered with one or more layers of the rubber.
Over time, the rubber printing blanket, due to constant and excessive use, inevitably deteriorates and becomes damaged. For example, the rubber printing blanket may become dented on its outer surface or lose its resiliency, thus adversely affecting the quality of the print. Whether the blanket becomes dented or damaged sometimes depends on the type of material onto which the image is transferred. Cardboard or heavy stock paper has been known to cause dents in the blanket more frequently than thinner papers.
A number of chemical products are currently available and widely used in the printing industry for repairing these rubber printing blankets. These products often contain chemicals such as methylene chloride, perchloroethane, 1,1,1-trichloroethane and other chlorinated solvents. The majority of these rubber swelling/blanket washing products contain methlyene chloride.
These products, also known as blanket washes, are usually brushed on the blanket causing the rubber blanket to swell to its original shape. Many of these washes also serve to remove the ink from the blanket. They quickly evaporate after being applied, thus leaving the blanket dry.
Many problems, however, are associated with the use of these blanket washes. For example, when applied to the blanket, residual amounts of these washes sometimes remain in the blanket, thus preventing the inked image from being properly transferred to the blanket. Also, since the washes are usually brushed on the blankets, brush marks usually are formed on the blankets.
Moreover, these chemicals, i.e., methylene chloride, perchloroethane and 1,1,1-trichloroethane, which are used to make these blanket washes, are highly flammable, highly toxic and require special handling. Their toxicity may create hazardous health problems in the work place, and also when disposed of, they can pollute the ground water. Further, these chemicals are known to cause ozone depletion in the earth's atmosphere.
In light of the Clean Air and Water Act, use of products containing these hazardous chemicals is being discouraged by lawmakers and environmentalists. Also, many businesses currently using these chemical products are looking for alternative chemical products which are environmentally safer and do not damage the ozone layer.
As discussed below, the embodiments of the present invention overcome and avoid the above problems associated with using these chemicals to swell rubber printing blankets.
N-methyl-2-pyrrolidone, shown below, otherwise known as M-PYROL.RTM. or NMP.RTM. (a registered trademark of GAF Chemicals Corporation of Wayne, N.J.) is a solvent which is used, for example, in nonflammable foams, rubber and vinyl adhesives, and as a stripper for epoxy resins and as a solvent for curing agents. ##STR1##
Mixtures of N-methyl-2-pyrrolidone and carboxypolymethylene are used in certain applications, namely stripping formulations, rubber and vinyl cements, and metal degreasing, where a gel-like consistency is desirable.
For example, N-methyl-2-pyrrolidone can be mixed with carboxypolymethylene to create an easy to handle, nonflowing epoxy paint stripper. To create this paint stripper, carboxypolymethylene is added very slowly to N-methyl-2-pyrrolidone. The mixture is agitated vigorously while heating below the flash point of the solvent (95.degree. C., 204.degree. F.). The mixture is then neutralized with di-2-ethylhexylamine.